Method of and a device for generating high pressures



April 9, 1963 c. BALLHAUSEN 3,084,388

METHOD OF AND A DEVICE FOR GENERATING HIGH PRESSURES Filed March 16, 1960 2 Sheets-Sheet 1 Fi l n in 2 1 l/ Fig. 4

April 9, 1963 c. BALLHAUSEN METHOD OF AND A DEVICE FOR GENERATING HIGH PRESSURES Filed March 16, 1960 2 Sheets-Sheet 2 Jnven/or: M0

United States Patent 3,084,388 METHOD 9F AND A DEVitCE FOR GENERATING HIGH PRESSURES Carl Ballhausen, Krefeld, Germany Filed Mar. 16, 19%, Ser. No. 15,383 Claims priority, application Germany Mar. 18, 1959 6 Claims. (Cl. i316.5)

The present invention relates to a method of and a device for generating high omnidirectional pressures inside a die, and to the use of said method and device, for in.- stance, for transforming a thermodynamically stable modification into a thermodynamically unstable modification of a substance, such as for instance of nitride of boron, carbon, and so forth. It has been found in actual practice that known and conventional apparatus of this kind, comprising for instance a conventional die cooperating with pressure members in the form of plungers or punches (hereinafter termed punches) for instance of hard metal, or the like, is at most capable of generating pressures which in order of magnitude do not exceed 400 kg./sq. mm. Pressures above 400 kg./sq. mm. cannot thus be obtained.

For the purpose of generating pressures, principally pressures exceeding 400 kg./ sq. mm. a plastically deformable cartridge may be inserted into a die, the hollow interior of the cartridge providing the actual pressure cavity for the reception therein of the substance that it is to be subjected to pressure and the cartridge compressed by the punches in such manner as to reduce its height as well as its internal diameter and thereby to diminish the capacity of the cavity in its interior. The punch in this case does not directly bear down on the substance which is to be subjected to pressure but acts through the intermediary of the flowing medium of a plastically deformable cartridge. The method permits the generation of pressures which substantially exceed the afore-mentioned 400 kg. sq. mm. and which act omnidirectionally upon the substance compressed inside the cavity.

The hereinafter described method proposed by the invention is also very well suited for the use and application of the aforesaid high pressures at considerably elevated temperature levels, preferably above 2000 C. In such a case the method is performed in such a way that the pressure is applied in the specified manner during or immediately after the substance that is to be subjected to pressure inside the cavity has been heated. Preferably the substance is heated in such a case by electric resistance heating, care being taken to see that a relatively large current flows through the substance that it is to be heated, in the shortest possible time. This can be done either by briefly switching on a transformer or by abruptly discharging a condenser battery adapted in capacity to the volume of the substance that is to be pressed. However, in principle, it would also be possible to make use of inductive heating.

In order to perform the method according to the invention various devices can be employed, which may be more or less complex according to the level of pressure it is desired to reach. In the simplest form of such a device a plastically deformable cartridge consisting for instance of soft annealed copper, unstable austenitic steel, or the like, is simply inserted into a conventional die.

The necessary pressure may be generated by a conventional press or by a press equipped with an accumulator. It will be understood that the press may as such be a mechanical, a hydraulic or any other desired type of press.

According to the method of the present invention, to permit even higher pressures to be obtained, it is proposed to dispense with pressure transmitting punches altogether and to employ merely a plastically deformable cartridge 3,684,388 Patented Apr. 9, 1963 ice which slightly projects from the edges of the cavity in the die. This is the amount whereby the plastically deform able cartridge will be compressed when it is used, so that the volume of the projecting portion of the cartridge will be equal to the maximum possible achievable diminution in capacity of the internal cavity in the cartridge.

In order to facilitate thrusting the projecting part of the cartridge into the die it has been found advantageous if high mechanical strength is imparted to this projecting part of the cartridge, whereas the portion of the cartridge which is embraced by the die should have low mechanical strength. This can be easily achieved, for instance, by using a material for making the cartridge which gains considerably in mechanical strength when cold worked, a property exhibited for instance by an unstable austinitic steel. To this end the entire cartridge may first be soft annealed and the projecting ends may then be strengthened by cold working. It is also preferred to taper the projecting parts of the cartridge towards their extremities. The result is the formation of a cylindrical cartridge of given thickness of wall with coned or rounded extremities.

In the simplest case the die may consist of an annular shell of considerable thickness into the interior of which the plastically deformable cartridge can be inserted. In order to permit the shell to absorb maximum possible pressures it has been found useful to form the shell of a plurality of interposed cylindrical sleeves or rings tightly pressed the one into the other. Either the rings may consist of different working materials which also have different strengths, or all the rings may be made of the same working material having different mechanical strengths, preferably increasing towards the innermost ring, in that the rings are subjected to different thermal treatments or cold working procedures.

The cheeks of the device which supplies the pressure, for instance the pressing plates of a press, may be armoured with hard metal, in a manner already known to the art, in those regions which are called upon to sustain the highest compressional stress.

If it is desired to heat the substance which has been inserted into the cavity inside the deformable cartridge to be subjected to pressure therein, then a deformable insulating material must be interposed between the plastically deformable cartridge and the compressed material inside the cartridge, for instance in the form of pressed and lightly sintered alumina. Tests performed by the inventor have shown that for this purpose a small tube of lightly sintered alumina or of some other lightly sintered oxide is especially suitable, said tube being inserted into the interior of the plastically deformable cartridge. It will be understood that the insulating material could be located elsewhere if circumstances permit, for example between the cartridge and the actual die. The electric current which in the manner described is conducted through the material inside the cavity of the cartridge is most conveniently applied through a specially provided supplementary punch. The manner in which this is performed will be described later by reference to the accompanying drawings. For insulating the parts of the die which carry no current from the current-carrying cheeks of the press, natural mica has been found to be very eifec-tive.

The accompanying illustrations show a number of embodiments of the device according to the invention in more or less schematic form.

FIG. 1 schematically shows a device in cross section which permits high pressure to be generated on a substance with the aid of relatively large pressure-applying punches.

FIG. 2 is a device in which a short portion of the punches projects from the die.

FIG. 3 is a device according to the invention which comprises no punches and in which the plastically deformable cartridge projects a given amount from both sides of the die.

FIG. 4 illustrates a special form of construction of the device according to FIG. 3.

FIG. is a device according to the invention in which various parts of the previously illustrated devices are combined in suitable manner.

In FIG. l]. the die proper is indicated by 1. Inserted into this die is the plastically deformable cartridge 2. 3 is the cavity inside the cartridge which contains the substance that is to be pressed. 4 and 5 are the pressureapplying punches which compress the plastically deformable cartridge. 6 indicates a sleeve or ring which embraces punch 5- in order to permit higher pressures to be applied by the punch to cartridge 2 than would be possible if such a sleeve were not provided. It will be understood that the provision of such a sleeve is not restricted to the lower end of the punches, as shown in FIG. 1, but that the whole of the pu-ches may thus be reinforced in the manner that has been described.

A device such as that illustrated in FIG. 1 does not permit of the generation of pressures which exceed the 400 kg./ sq. mm. mark by a considerable margin.

A suitable device for the generation of higher pressures is that schematically shown in FIG. 2. T he die is again indicated by 1, 2 being the plastically deformable cartridge, 3 its hollow interior, and 4 and 5 the punches which are practically completely contained in the die 1, projecting by a small amount only. This amount 7 exactly represents the distance the punches 4 and 5 will be subsequently forced into the die. The diameter of the punches 4 and 5 is carefully calculated to leave a given clearance 8 inside the die 1. This clearance is necessary in order to compensate the unavoidable expansion of the punches 4 and 5 when they transmit very high pressures. The clearance is so determined that at the desired pressure the punches will just fit tightly inside the walls of the die.

FIG. 3 shows a form of construction of a device according to the invention. It will be seen that in this in stance the punches have been dispensed with. Instead, the plastically deformable cartridge 2 projects a given distance 9 from each end of the die 1. This is the amount by which the cartridge will be subsequently compressed between the cheeks 10 of a press. As has been mentioned, the cartridge consists of a material of low mechanical strength but of the highest possible plasticity, such as a non-stable austenitic steel. The portions 11 which project from the die have a greater strength imparted to the material by cold working. Naturally, other materials would also be eligible for making the cartridge, provided the required differences in mechanical strength can be achieved by cold deforming or thermally treating the material. In the course of tests performed by the inventor cold working of non-stable austenitic steels was found to give especially satisfactory results.

FIG. 4 is a schematic representation of a form of device contrived in the manner illustrated in FIG. 3. This is suitable, for instance, for transforming graphite into diamond. 1 again represents the die but no details are shown in the drawing. Inside the die is the plastically deformable cartridge 2. The portions shaded with simple parallel lines have a lower mechanical strength, whereas high strength has been imparted to the cross-hatched portions in the above described manner. In order to permit the compressed material inside the cartridge to be heated during the applicationof pressure, the hollow interior of the cartridge is lined with an insulating tubelZ. This insulating tube may consist for instance of pressed or lightly sintered alumina. In order to reduce the diameter of the sample in relation to the covering disc 14 to 16, a second insulating tube is inserted into the first. This is denoted by 13. This second small tube must not react with the sample. In the present instance it consists of pressed powdered boron or silicon carbide. 14, 15 and 16, 17 are discs, i.e., circular plates, which serve the purpose of conducting the electric current to the material which is to be heated and subjected to pressure. The two discs 14 and 16 consist of a material which is a good conductor of electricity but which in the prevailing conditions of temperature and pressure will not react or alloy with the material that is to be compressed. If the material that is to be subject to pressure is carbon, say in the form of graphite, then the two plates 14 and 16 may with advantage likewise be graphite. In such a case the two plates 15 and 17 may consist, for instance, of metallic tungsten. Cavity 3 contains the material which is to be subjected to the high pressure. As has already been repeatedly stated the cubic capacity of the cavity will be reduced by the amount of volumetric compression of the plastically deformable cartridge 2. In order that this process may be more clearly understood it will be illustrated by working a numerical example.

In the device shown in FIG. 4 a cartridge was used having a diameter of 15 mm. and a height of 13 mm, the diameter of the central bore being 10 mm. This cartridge was inserted into a die which was 10 mm. thick. In other words 3 mm. of the cartridge projected, that is to say 1.5 mm. projecting from each side of the die.

The volume of the projecting portion of the cartridge is 15 g-3=530 cub. mm.

The initial cavity in the cartridge is 10 -g-13=1020 cub. mm.

This cavity is reduced by 530 cub. mm. when the cartridge has been compressed, i.e., to 48% of its former capacity. Of course, this is correct only on the supposition that the die will not yield when acted upon by the high lateral pressure. However, even assuming that the diameter will increase from 15 mm. to 15.6 111111., then the reduction in volume of 530 cub. mm. by an amount of 15-11-03 l0=l4l cub. mm. to 389 cub. mm. Will still lead to a reduction in the capacity of the cavity to 62% of its original size.

. FIG. 5 schematically illustrates an arrangement for the generation of ultra-high pressures, far in excess of 400 lag/sq. nun, at temperatures over 2000 C. This arrangement is based on the scheme described with reference to and illustrated by FIG. 4. 1 is the die which in this case is built up of a plurality of concentric rings 18, 19, 20, 21' and 22 which have been pressed the one into the other. These rings may be made, for instance, of a steel which has been submitted to a previous thermal treatment or which has been cold worked in such manner that the rings have increasing strength progressively to the inside. Hence ring 18 has the lowest mechanical strength and ring 22 is the strongest. 2 is the plastically deformable cartridge with portions ll projecting from both sides of the die 1 and having considerably higher strength than the centre portion inside the die. The pressure for plastically deforming the cartridge is applied by punches 4 which are reinforced by pressure-absorbing rings 6. In the embodiment illustrated in FIG. 5 these rings 6 likewise consist of concentrically interposed rings of progressively greater mechanical strength the further inside they are located. The bottom punch 4 is contrived in the same manner as the upper punch 4. Inter-posed between the plastically deformable cartridge and the material which it is intended to subject to pressure is an insulating material 12in the shape of'a tube of lightly sintered alumina as above mentioned. In the present embodiment the object of this tube is 'to insulate the pressure-applying punches 4 from the current-conducting punches 23, 24, 25 and 26 which will be later described. 13 is a supplementary insulating tube the object of which has already been explained. In

the cavity 3 is the substance which is to be subjected to pressure and heat. Current is supplied to this substance through the plates 27, cheeks 28, punches 23, 24 and 25, 26 and finally through the circular discs 14, 15 and 16, 17. In order to prevent the current from flowing through the pressureapplying punch 4 and the plastically deformable cartridge 2 an intermediate layer is provided at 30 and 31, which consists of an electrically well insulating material not deformable under compression, preferably natural mica. As is known as such, the punches 28 consist of steel or of some other hard material with hard metal reinforcements inserted at those points Where the highest compressional stresses arise. Naturally, the cheeks may likewise consist of pressed concentrically interposed ring of increasing hardness towards the inside. The punches 23 and 25 are tungsten pins firmly pressed into the hard metal portions 29.

Pressing with the aid of a narrangement contrived as schematically illustrated in FIG. 5 proceeds approximately as follows:

When the die, as illustrated in FIG. 5, has been assembled and fitted in the press, the compressing cheeks of the press are closed and the pressure is raised to the level required by the purpose in view. During the application of pressure a low current is passed through the assembly and the variation in resistance checked by measuring the voltage, more particularly in order to ensure that no short circuit has arisen. The pressure obtained is maintained by means of a pressure accumulator. The source of current, such as a transformer, connected with the copper electrodes 27, is now briefly switched on. This current principally generates heat in the sample contained in the internal cavity 3, the circular discs 14-17 being naturally heated to a lesser extent. When the sample changes into a different modification its volume suddenly contracts and this would cause a simultaneous abrupt reduction in pressure unless the press were provided with appropriate means which are adapted to respond within a very short time and absorb the pressure drop so that substantially the applied pressure will be maintained.

Under the influence of the ultra-high pressure and of the high temperature substances which are in a thermodynamically stable modification can frequently be successfully transformed into a thermodynamically unstable modification. For instance, if the internal cavity 3 is filled with graphite having a density of between 2.00 and 2.25 and the above described procedure is then performed, the graphite will be transformed into pure diamond having a density of 3.50. This corresponds with a reduction in the volume of the sample to 64% of its original volume. Since the other components of the assembly cannot be substantially compressed the reduction in the capacity of the internal cavity which has above been determined by calculation will therefore suffice for achieving the contemplated result.

It will be readily understood that the utility of the invention is not confined to the transformation of graphite into diamonds. Other transformations of one modification into another are likewise possible. For example the thermodynamically stable modification of boron nitride can be transformed into the thermodynamically unstable modification which is of technological interest in several respects. The method and the device proposed by the invention can be utilised whenever it is desired to change one modification of a substance into another at elevated or room temperature by the compression of the stable modification to an extent which was hitherto impossible to achieve or impossible adequately to control.

If the sample in question should be electrically nonconducting, then a Wire, ribbon or small tube of a highmelting metal may be inserted into the same.

What I claim is:

1. A device for generating increased high omnidirectional pressure on a substance to be compressed, comprising a die and 1a plastically deformable metallic cartridge which fits into the die and projects from the ends thereof and opposed pressure members having pressure-producing faces to contact the ends of the cartridge and compress this wholly in the die, the portion of the cartridge that projects from the die having high mechanical strength compared with the portion which fits inside the die.

2. A device according to claim 1 in which said metallic cartridge is of an unstable austenitic steel.

3. A device according to claim 1 having a said projecting portion at each end of the metallic cartridge which tapers towards the end of the cartridge.

4. A device according to claim 1 comprising pressure members surfaced with hard metal where the compressional stresses are at a maximum.

5. A device according to claim 1, said metallic cartridge having a lining of deformable insulating material and a supplementary lining of material of low electrical conductivity which will not react with the substance that is to be compressed, said supplementary lining defining the axial length and cross-sectional area of a cavity shorter than the length of the cartridge to receive the substance to be compressed.

6. A device according to claim 1, said metallic cartr-idge having lining means of deformable insulating material defining the wall of a cavity to receive the substance to be compressed in said cartridge, said pressure members being tubular members having a lining of insulating material, further members to apply pressure to the said pressure members, electrically conductive members between the further members and the substance to be compressed in the said cavity, and insulating layers between the said further members and the said tubular pressure members, said conductive members being such as not to react or alloy with the said substance during the conditions prevailing when the substance is electrically heated and is compressed in the said cavity.

References Cited in the file of this patent UNITED STATES PATENTS 1,122,280 Kempshall Dec. 29, 1914 2,941,243 Bundy June 21, 1960 2,941,248 Hall June 21, 1960 2,941,252 Bovenkerk June 21, 1960 2,947,610 Hall et a1. Aug. 2, 1960 OTHER REFERENCES Bovenkerk et al.: Nature 184, 1094-1098 (1959). 

1. A DEVICE FOR GENERATING INCREASED HIGH OMNIDIRECTIONAL PRESSURE ON A SUBSTANCE TO BE COMPRESSED, COMPRISING A DIE AND A PLASTICALLY DEFORMABLE METALLIC CARTRIDGE WHICH FITS INTO THE DIE AND PROJECTS FROM THE ENDS THEREOF AND OPPOSED PRESSURE MEMBERS HAVING PRESSURE-PRODUCING FACES TO CONTACT THE ENDS OF THE CARTRIDGE AND COMPRESS THIS WHOLLY IN THE DIE, THE PORTION OF THE CARTRIDGE THAT PROJECTS FROM THE DIE HAVING HIGH MECHANICAL STRENGTH COMPARED WITH THE PORTION WHICH FITS INSIDE THE DIE. 